Polycythemia vera (PV), idiopathic myelofibrosis (IMF), chronic myelogenous leukemia (CML) and essential thrombocythemia (ET) are classified as the chronic myeloproliferative disorders because their pathophysiology involves the clonal expansion of a multipotent hematopoietic progenitor cell with the over-production of one or more of the formed elements of the blood (1,2,3,4). However, with the exception of CML, these disorders lack a clonal marker, their pathogenesis is unknown, and their diagnosis therefore is dependent upon clinical criteria. Remarkably, in spite of their origin from a transformed clone, the mature circulating blood cells in these disorders are morphologically normal and, in contrast to CML, progression to acute leukemia is far less common in PV, ET and IMF. Furthermore, while these latter disorders can mimic each other clinically, they have distinctly different clinical courses and differ with respect to their treatment. Therefore, the identification of a diagnostic marker would be very useful.
Polycythemia vera is the commonest of the chronic myeloproliferative disorders and although its hallmark is trilineage hyperplasia, erythrocytosis is its most prominent clinical manifestation. For this reason, most investigators have focused on erythropoiesis in PV in an attempt to define its etiology but without notable success. There is a need in the art for diagnostic methods for distinguishing PV from other diseases involving erythrocytosis.